Cyclosporin A (CsA), a neutral cyclic undecapeptide isolated from the fungus Tolypocladium inflatum and currently marketed as NEORAL ® and SANDIMMUNE ® (Novartis, Basel, Switzerland), has been widely used for the prevention of organ transplant rejection. The molecular basis for the immunosuppressant activity of cyclosporin A and cyclosporin analogues begins with the passive diffusion of the cyclosporin (Cs) molecule into the cell, followed by binding to its intracellular receptor, cyclophilin A (CypA). CypA belongs to a family of proteins that catalyze cis-trans peptidyl-prolyl isomerization, i.e., PPIase, a rate-limiting step in protein folding. CsA and other cyclosporin analogues bind to the active site of CypA. However, immunosuppression is not believed to be due to the inhibition of CypA PPIase activity. The target of the CsA-CypA complex is a Ca2+-calmodulin-dependent serine-threonine-specific protein phosphatase, calcineurin. In T-cells responding to antigen presentation, an increase in intracellular Ca2+ activates calcineurin, which subsequently dephosphorylates the transcription factor called the nuclear factor of activated T-cells (“NFAT”). Dephosphorylated NFAT undergoes a molecular change, e.g., homodimerization that allows it to cross into the nucleus, and promotes the expression of T-cell activation genes. CsA and other immunosuppressive cyclosporin derivatives inhibit calcineurin which results in the inhibition of expression of cytokine genes, e.g., interleukin-2 (IL-2) that promotes T-cell activation and proliferation, i.e., immunosuppressive activity.
Human Immunodeficiency Viruses and Cyclosporin A or Non-Immunosuppressive Cyclosporins
Human immunodeficiency viruses (“HIVs”) are lentiviruses, a family of mammalian retroviruses evolved to establish chronic persistent infection with gradual onset of clinical symptoms. There are two major families of HIV. Most of the epidemic involves HIV-1; HIV-2 is a close relative whose distribution is concentrated in western Africa.
Human cyclophilins A and B have been identified as cellular proteins which bind specifically to HIV-1 Gag polyprotein, p555gag. Gag proteins play a major role in several steps of the virus life cycle, including the assembly and release of virions (Willis et al., “Form, Function, and Use of Retroviral Gag Proteins,” AIDS 5:639-654 (1991)). A cleavage product of the Gag polyprotein, the capsid protein, has been shown to bind specifically to cyclophilin A. Cyclophilin A is functionally associated with the HIV-1 virions through interaction with the Gag polyprotein. This interaction between cyclophilin A and Gag proteins is inhibited by the immunosuppressive drug, cyclosporin A (Thali et al., “Functional Association of Cyclophilin A With HIV-1 Virions,” Nature 372:363-365 (1994)).
Cyclosporin A has demonstrated in vitro antiviral activity against HIV-1 (Karpas et al., “Inhibition of Human Immunodeficiency Virus and Growth of Infected T-cells by the Immunosuppressive Drugs Cyclosporin A and FK 506, ” Proc. Natl. Acad. Sci. USA 89:8351-8355 (1992)); however, initial in vivo studies in which cyclosporin A was administered as a monotherapy in HIV-infected patients at advanced stages of disease did not show a beneficial effect from the treatment (Levy et al., “Long-Term Follow-Up of HIV Positive Asymptomatic Patients Having Received Cyclosporin A,” Adv. Ex. Med. Biol. 374:229-234 (1995)). U.S. Pat. No. 4,814,323 to Andrieu et al. reported that administration of cyclosporins may be used for the prevention of AIDS in patients infected with the virus before the appearance of the AIDS symptoms, that is patients with no symptoms or patients with AIDS related complex.
Highly active antiretroviral therapy (“HAART”) has dramatically decreased the HIV-related morbidity and mortality rates among HIV-infected patients and the transmission of HIV from mother to child by efficiently suppressing viral replication (Palella et al., “Declining Morbidity and Mortality Among Patients With Advanced Human Immunodeficiency Virus Infection,” N. Eng. J. Med. 338:853-860 (1998)). Limitations of HAART have become better understood. Thus, the virus can be suppressed to undetectable levels but not eradicated. In addition, there is an ever-growing list of side effects, the eventual development of resistance, and the cost and complexity of HAART regimens that must be contended with.
HAART covers a broad range of antiretroviral agents that include nucleoside reverse transcriptase inhibitors (“NRTI”), nonnucleoside reverse transcriptase inhibitors (“NNRTI”), HIV protease inhibitors, and fusion inhibitors. Specific examples of antiviral agents from each of these families include: Zidovudine, Didanosine, Stavudine, and Lamivudine from the NRTI antiviral class; Nevirapine, Efavirenz, and Delavirdine from the NNRTI antiviral class; Saquinovir, Indinavir, and Ritonavir from the HIV protease inhibitor class; and Enfuvirtide from the fusion inhibitor antiviral class.
From an immunological standpoint, the introduction of HAART allows for only a partial immune reconstitution. Indeed, ex vivo measures of immune function do not generally normalize and, most importantly, HIV-specific T cell responses remain almost invariably impaired. Though several variables have been identified that correlate with the degree of immune reconstitution during HAART, the actual underlying mechanism(s) responsible for such an incomplete immune reconstitution are still poorly understood and likely reflect the severe HIV-driven perturbations in T cell dynamics and homeostasis and the interaction between host and viral factors (Douek, “Disrupting T-Cell Homeostasis: How HIV-1 Infection Causes Disease,” AIDS Rev. 5:172-177 (2003)).
A strategy aimed at the broadest immune reconstitution, possibly overcoming the limitations of HAART, consists in the adjuvant use of immunomodulants. By combining cyclosporin A with HAART, the goal is to contain the immune activation, either virus-specific or owing to non-specific “by-stander” activation. Results from pilot studies in HIV-infected patients has shown that the rapid shutdown of T-cell activation induced by cyclosporin A has produced a more rapid and stable increase in CD4+ T-cells and a significant long-term increase in IFN-γ secreting CD4+ and CD4+CCR7− T-cells, establishing a more favorable immunological set-point (Bandera et al., “Immunomodulants in HIV Infection,” Expert Opin. Ther. Patents 15(9): 1115-1131 (2005)). Determination of the long-term efficacy must be assessed in order to understand if this approach truly has value.
SDZ NIM 811 is a cyclosporin analogue that is completely devoid of immunosuppressive activity but exhibits potent and selective anti-HIV-1 activity (Mlynar et al., “The Non-Immunosuppressive Cyclosporin A Analogue SDZ NIM 811 Inhibits Cyclophilin A Incorporation Into Virions and Virus Replication in Human Immunodeficiency Virus Type-1-Infected Primary and Growth-Arrested Cells,” J. General Virology 78:825-835 (1997)). SDZ NIM 811 does not prevent the activation of CD4+ T-cell activation as cyclosporin A does. In a manner similar to cyclosporin A, it is proposed that SDZ NIM 811 interferes with the HIV-1 Gag-cyclophilin A interaction to effect its antiviral activity.
SDZ NIM 811 does not inhibit calcineurin and possesses none of the immunosuppressive activity of cyclosporin A. The potent inhibition of calcineurin by cyclosporin, in addition to being responsible for the potent immunosuppressive activity of cyclosporin A, is also believed to be the cause of the toxicity and the narrow therapeutic index of this drug. Separation of immunosuppressive and antiviral activity could lead to novel antiviral cyclosporins with fewer side effects and improved therapeutic index. Elucidation of structure activity relationships for cyclosporins permits the design of non-immunosuppressive cyclosporin derivatives that retain potent (cyclophilin A) PPIase activity to achieve this goal (Bartz et al., “Inhibition of Human Immunodeficiency Virus Replication by Non-Immunosuppressive Analogs of Cyclosporin A,” Proc. Natl. Acad. Sci. USA 92:5381-5385 (1995)). European Patent No. 484 281, U.S. Pat. No. 5,767,069, U.S. Pat. No. 5,948,884, and French Patent Nos. 2,757,520, 2,757,521, and 2,757,522 disclose non-immunosuppressive cyclosporins with antiviral activity.
Hepatitis C Virus and Cyclosporin A
Recently, cyclosporin A, the most widely prescribed immunosuppressive drug, was reported to be clinically effective against hepatitis C viral (HCV) infection (Nakagawa et al., “Specific Inhibition of Hepatitis C Virus Replication by Cyclosporin A,” Biochem. Biophys. Res. Commun. 313:42-47 (2004)). The authors of the Nakagawa et al. paper state that certain chaperone activities, such as those of cyclophilins, may be crucial for the processing and maturation of the viral proteins and for viral replication.
A subsequent controlled clinical trial showed that a combination of cyclosporin A with interferon α2b is more effective than interferon monotherapy, especially in patients with high viral loads (Inoue et al., “Combined Interferon α2b and Cyclosporin A in the Treatment of Chronic Hepatitis C: Controlled Trial,” J. Gastroenterol. 38:567-572 (2003)).
PCT International Patent Publication No. WO 2006/005610 recently described the use of a combination of cyclosporin A and pegylated interferon for treating hepatitis C viral infection. In addition, PCT International Patent Publication No. WO 2005/021028 relates to the use of non-immunosuppressive cyclosporins for treatment of HCV disorders. Also, Paeshuyse et al., “Potent and Selective Inhibition of Hepatitis C Virus Replication by the Non-Immunosuppressive Cyclosporin Analogue DEBIO-025, ” Antiviral Research 65(3):A41 (2005) recently published results for a non-immunosuppressive cyclosporin analogue, DEBIO-025, that exhibited potent and selective inhibition of hepatitis C virus replication. Notably, the cyclosporin derivative DEBIO-025 is also effective for the treatment of HIV-1 (Rosenwirth et al., “Debio-025, A Novel Non-Immunosuppressive Cyclosporine Analog with Potent Anti-Human Immunodeficiency Virus Type 1 Activity: Pharmacological Properties and Mode of Action,” Antiviral Research 65(3):A42-A43 (2005)). Debio-025 does possess potent binding affinity for cyclophilin A.
There is still a large need for novel cyclosporin analogues that have therapeutic utility in the treatment of viral-induced diseases.
The present invention is directed to achieving these objectives.